Device for melting snow or ice

ABSTRACT

An installation for melting of snow or ice, e.g. at roof downpipes on flat roofs, in gutters and the like, comprising a heating means (11), a temperature sensor means (4,6) and a control unit (1) for connecting and disconnecting the heating means (11) in dependence on sensed temperature. The temperature sensor means comprises a first temperature sensor (4) for sensing the surface temperature at the place of snow or ice melting, and a second temperature sensor (6) for sensing the air temperature at the topical place. On the surface there is further arranged a snow sensor (7) which is connected by the control unit (1) when the first temperature sensor (4) at a rising temperatures registers that the surface temperature rises above a chosen minus value, or when the second temperature sensor (6) at a falling temperature registers that the air temperature falls below a chosen plus value, the control unit (1) causing connection of the heating means (11) if the snow sensor (7) registers snow during a chosen time period, and further keeping the heating means (11) connected at least until the second temperature sensor (6) at a rising temperature registers that the air temperature rises above the chosen plus value, or at least until the first temperature sensor (4) at a falling temperature registers that the surface temperature falls below the chosen minus value, but in both cases only on the condition that the snow sensor (7) at intervals registers snow.

The invention relates to an installation for melting of snow or ice,especially on roofs, in roof downpipes and gutters, and around manholesin roadways and the like, comprising a heating means, a temperaturesensor means and a control unit for connecting and disconnecting theheating means in dependence on sensed temperature.

BACKGROUND OF THE INVENTION

There are previously known different embodiments of control systems forthe control of heating cables or the like for snow and ice melting atroof downpipes, in gutters and the like. In principle, two controlsystems are on the market today. One of these measures the airtemperature and connects heating cables in an adjustable temperatureinterval, e.g. between -5 and +5° C. The other system measures an airtemperature and combines this with a water sensor in a gutter, and aheating cable is kept connected as long as the temperature is below themelting point at the same time as the water sensor registers moisture inthe gutter.

The weakness of the first system is that it uses much current. Thesecond system will be connected as long as one has minus degrees andsnow. However, much dirt always gathers in gutters, something which mayrapidly cause errors in the water sensor registration.

SUMMARY OF THE INVENTION

The object of the present invention is to provide an installation whichin an efficient manner prevents ice formation and thereby ensures a freewater passage at the introductorily mentioned places, and which is veryeconomic in operation, the power consumption being very low as comparedto installations according to the prior art.

The above-mentioned objects are achieved with an installation of theintroductorily stated type which, according to the invention, ischaracterized in that the temperature sensor means comprises a firsttemperature sensor for sensing the surface temperature at the place ofsnow or ice melting, and a second temperature sensor for sensing the airtemperature at the topical place, and that a snow sensor is arranged onsaid surface, which sensor is connected by the control unit when thefirst temperature sensor at a rising temperature registers that thesurface temperature rises above a chosen minus value, or when the secondtemperature sensor at a falling temperature registers that the airtemperature falls below a chosen plus value, the control unit causingconnection of the heating means if the snow sensor registers snow duringa chosen time period, and further keeping the heating means connected atleast until the second temperature sensor at a rising temperatureregisters that the air temperature rises above the chosen plus value, orat least until the first temperature sensor at a falling temperatureregisters that the surface temperature falls below the chosen minusvalue, but in both cases only on the condition that the snow sensor atintervals registers snow.

A principal feature of the installation according to the invention isthat there are used two temperature sensors for controlling connectionand disconnection of the heating means of the installation, usually aheating cable, namely a first sensor for sensing the surface temperatureat the topical place, e.g. a roof surface, and a second sensor forsensing the air temperature at the place. As known, the temperature at aroof surface of a building will be more or less above the temperature ofthe ambient air because of the heat from the roof. The temperaturedifference between the surface temperature and the air temperature willnever be constant, but will vary with the snow quantities on the roofand the moisture content in the snow. In addition, it will vary betweendifferent buildings, dependent on insulation and ventilation. In theinstallation according to the invention, both said temperatures aremeasured, so that the operation of the installation is made independentof variations in said temperature difference. One achieves thereby thatthe heating cable of the installation is only connected in the periodswherein there is a need for this, viz. when the air temperature is inthe range between 0° C. and the minus value at which the surfacetemperature at the topical place, e.g. a roof surface, is equal to 0° C.

BRIEF DESCRIPTION OF THE DRAWING

The invention will be further described below in connection withexemplary embodiments with reference to the drawings, wherein

FIG. 1 shows a principle drawing of an installation according to theinvention;

FIG. 2 shows a schematic view of a control panel which may form part ofthe installation; and

FIG. 3 shows a schematic sectional view of a roof downpipe wherein thereis fitted an installation according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The installation shown in FIG. 1 comprises a control unit 1 in the formof an electronics part to which the different sensors and otherequipment forming part of the installation, are connected. The controlunit is constituted by a box containing different electric/electroniccircuits for operation and control of the installation, so that thisworks in the manner described below. The circuits are constructed tocomply with particular operational specifications and are based onconventional technique with which an expert in the topical field will befamiliar. A further description of the construction and operation ofthese circuits is not considered to be necessary for the understandingof the invention, and is therefore not included in the presentdescription.

As appears from FIG. 1, the control unit 1 has an input 2 for connectionof operating voltage, i.e. normally 220 V alternating voltage. A line 3leads to a first temperature sensor 4 for sensing the surfacetemperature at the place where snow and/or ice is to be melted, e.g. aroof surface, and a second line 5 leads to a second temperature sensor 6for sensing the air temperature at the topical place. Said lines consistof cables of suitable length and quality. To the unit there is furtherconnected a snow sensor 7 consisting of a suitable heating cable 8 and awater sensor or water detector 9 which is connected to the unit via asuitable cable 10. The water sensor e.g. may consist of a pair ofacidproof pins.

The heating means of the installation consists of a heating cable 11,e.g. of maximum 3,6 kW, which is connected to the control unit via acable 12.

To the control unit 1 there is also connected a water level sensor 13which has the task to warn if gutters become filled with water. Further,the control unit has an input 14 for connection of an extra surfacetemperature sensor, and an input 15 for connection of an extra snowsensor. There is also arranged an input 16 for connection of a switch(23 in FIG. 3) for manual forced control, i.e. connection of theinstallation for e.g. 24 hours irrespective of the temperatureconditions. Finally, the control unit is provided with an input 17 forconnection of a control panel for inspection and control of thedifferent installation functions.

FIG. 2 shows an embodiment of the control panel which is designated 20.The panel has an output 21 for connection of a suitable multicore cable22 leading to the input 17 of the control unit. On the panel there isarranged a number of switches, more specifically a switch 23 forconnection and disconnection of the installation, a switch 24 for theabove-mentioned forced control of the installation, and a switch 25 forresetting of the installation after a water level alarm (warned by meansof the sensor 13). There is also arranged a switch 26 for automaticdisconnection of the entire installation when the air temperature sensor6 registers a temperature exceeding a certain limit, e.g. +5° C. Therebyoverheating of the roof covering is avoided if the heating cable shouldbe connected through a fault.

The panel further includes a number of monitor lamps, e.g. lightemitting diodes, more specifically a lamp 27 (green) which is lightedwhen the installation is connected, a lamp 28 (blue) which is lightedwhen the snow sensor 7 is connected, a lamp 29 (yellow) which is lightedwhen the main heating cable 11 is connected, and a lamp 30 (red) whichis lighted when a water level alarm is delivered. In addition tolighting of the lamp 30 with such an alarm, there is also delivered anaudio signal from a buzzer 31.

The control panel 20 in addition has an output 32 for forwarding thewater level alarm to a plant for central operations control, and also anoutput 33 for a loudspeaker or a siren.

FIG. 3 shows a schematic sectional view of a part of a flat roof 40 werean installation according to the invention is fitted in connection witha roof rainwater outlet having an internal downpipe. As appears, theroof is insulated by an insulation 42 which is covered by a roofcovering 43. The roof outlet is covered by a gully cap 44.

The control unit 1 of the installation is shown to be fastened to a roofelement 45, but it may instead e.g. be fitted at a remote central place,possibly for the control of heating means at different places. Thecontrol unit is connected via respective lines with the heating means11, with the snow sensor 7, with the surface temperature sensor 4 andwith the air temperature sensor 6. The heating means may consists of aheating carpet or of a suitable arrangement of one or more heatingcables arranged around the gully 41. The different sensors are fitted ata suitable distance from the gully.

The manner of operation of the installation will be further describedbelow, and firstly in the case in which the temperature is rising.

The temperature sensor 4 measures the surface temperature of the roofsurface and connects the snow sensor 7, i.e. the heating cable 8 and thewater detector 9, when the temperature rises and passes a chosen valueof -0,4° C. If the water detector 9 registers water during a period of30 minutes after connection, the main heating cable 11 is connected bythe control unit 1, and at the same time the heating cable 8 of the snowsensor is disconnected. The main heating cable remains connected untilthe air temperature sensor 6 registers that the air temperature hasrisen to a chosen value of +0,4° C. This is, however, conditioned by thefact that the snow sensor 7 at intervals registers snow at the roofsurface. For this reason the water detector 9 is connected again for achosen time period of 10 minutes every four hours after the firstdisconnection. (In this case the snow sensor heating cable 8 is notconnected.) If water is registered during said time period, the mainheating cable 11 shall still be connected. If, however, water is notregistered in the course of the period (10 min.), the heating cable isswitched off even if the air temperature has not reached +0,4° C.

When the temperature is falling, the manner of operation is as follows:

When the air temperature sensor 6 registers that the air temperaturefalls below the chosen value of +0,4° C., the snow sensor 7 isconnected, which sensor controls if there is snow on the roof, in amanner corresponding to that described above (the heating cable 8 andthe water detector 9 are connected for 30 min.). If snow is notregistered, the installation becomes torpid. If snow is registered, themain heating cable 11 is connected and remains connected until thesurface temperature. sensor 4 registers that the surface temperaturefalls below -0,4 ° C. At the same time as the heating cable 11 isconnected, the water sensor 9 checks if water still arrives, morespecifically for ten minutes every four hours. If water is notregistered, the heating cable is switched off.

The above-mentioned function of the installation in case of fallingtemperature shall be able to be disconnected by means of a switch (notshown) in the control unit. This is important for current saving whenthe installation is used on glass roofs.

It should be noted that the stated temperature limits of ±0,4° C. forthe current sensors are chosen as a safety margin to ensure that theinstallation is not connected too late or disconnected too early becauseof inaccuracy in the meters. It may also be appropriate to use a largersafety margin, e.g. ±1 ° C. If quite accurate temperature meters arepresupposed, the temperature limits will be ±0° C.

In addition to the above-mentioned functions, the control unit may alsobe arranged to disconnect the main heating cable 11 only after a chosentime period after said chosen temperature limit has been registered bythe topical temperature sensor. This time period may be adjustable, e.g.in steps of one hour for up to 6 hours. In this manner one may pick upor compensate for variations in the construction or in the snow depth.For example, it is not sure that the surface temperature sensor willalways be fitted were the heat loss is greatest. Further, the airtemperature sensor may be subjected to an unintentional heat influence,e.g. from a window which is opened.

I claim:
 1. An installation for melting of snow and ice, especially onthe surface of roofs, roof downpipes and gutters, and around manholes inroadways and the like, comprising:a heating means for melting snow orice on said surface; a temperature sensor means comprising a firsttemperature sensor for sensing the temperature of said surface, and asecond temperature sensor ambient air temperature at said surface; acontrol unit for connecting and disconnecting said heating means independence on the temperatures sensed by said temperature sensors; and asnow sensor arranged on said surface and connected to said control unit,said control unit being arranged to connect said snow sensor when saidfirst temperature sensor at a rising temperature registers that thesurface temperature rises above a chosen minus value, or when the secondtemperature sensor at a falling temperature registers that the airtemperature falls below a chosen plus value, the control unit causingconnection of the heating means of the snow sensor registers snow duringa chosen time period, and further keeping the heating means connected atleast until the second temperature sensor at a rising temperatureregisters that the air temperature rises above the chosen plus value, orat least until the first temperature sensor at a falling temperatureregisters that the surface temperature falls below the chosen minusvalue, but in both cases only on the condition that the snow sensorregisters snow during said chosen time period.
 2. Installation accordingto claim 1, CHARACTERIZED IN that the chosen time period in which thesnow sensor (7) has to register snow, is 30 min.
 3. Installationaccording to claim 1 or 2, CHARACTERIZED IN that the chosen minus valueof the surface temperature is in the range 0° C. to -1° C., and thechosen plus value of the air temperature is in the range 0° C. to +1° C.4. Installation according to claim 3, CHARACTERIZED IN that the minusvalue is about -0,4° C. and the plus value is about ±0,4° C. 5.Installation according to claim 1, characterized in that the controlunit (1) is arranged to disconnect the heating means (11) only after achosen time period after that said chosen temperature limit isregistered by the topical temperature sensor (4 or 6).
 6. Installationaccording to claim 5, CHARACTERIZED IN that the chosen time period isadjustable, e.g. in steps of one hour for up to 6 hours.
 7. Installationaccording to claim 1, characterized in that the control unit (1) isarranged to disconnect the snow sensor (7) simultaneously withconnection of the heating means (11).
 8. Installation according to claim7, CHARACTERIZED IN that the control unit (1) is arranged to connect thesnow sensor (7) again for a chosen time period, e.g. of 10 min., everyfour hours after said disconnection.
 9. Installation according to claim1, characterized in that it is provided with a switch (26) forautomatically interrupting the voltage supply to the installation whenthe second temperature sensor (6) senses an air temperature exceeding acertain limit, e.g. +5° C.
 10. Installation according to claim 1,characterized in that it includes a control panel (20) having switches(23-26) and lamps (27-30) for supervision and inspection of thedifferent installation functions.